When i offset a curve e.g. a circle that's is not in the xy/xz/yz-planes it results in a complex curve that seems to be aequidistant to the original curve always measured in the xy-plane.

If i offset a curve that is in one of the system planes, depending on the viewport in which i have my cursor, the offset is either perpendicular to the curve's plane or coplanar with the original curve.

Is all this intended behaviour? What would i have to do to e.g. offset a circle that is outside of a system plane so that the offset curve is coplanar with the original?